ActivityPub: a federated protocol with formal change rules

The W3C repository presents ActivityPub, a decentralized social networking protocol that combines a client-to-server API with a federated server-to-server API. Built on the ActivityStreams 2.0 JSON-LD format, it supports extensible activity descriptions and different kinds of social applications.

The repository also explains how to evolve a published recommendation: clarifications belong in the Primer, corrections follow an errata process, and breaking changes require a new working group. That formal governance reflects the deployment cost of changing a protocol used by many independently operated servers.